This invention relates to storage tanks and more particularly to storage tanks for compressed natural gas (CNG).
Natural gas, commonly known as methane gas, is a mixture of low molecular weight hydrocarbons obtained in petroleum-bearing regions throughout the world. It is generally composed of about 85 weight percent methane, 10 weight percent ethane, and the balance being made up of propane, butane and nitrogen. As part of its overall national energy policy, the Department of Energy (DOE) is considering CNG as an alternative fuel. CNG is being considered to be used as fuel for fleet cars, light duty vehicles, taxis and school buses. Some groups in the railroad industry are experimenting with natural gas to power their locomotives.
CNG storage tanks comprise pressure vessels which can withstand a service pressure of up to 5,000 psi (34,500 kPa). A pressure vessel typically comprises an outer structural shell provided with an inner liner. The outer shell provides strength for pressurization of the vessel while the liner prevents the gas from leaking out. Currently used inner liners are made of aluminum or steel. However, aluminum and steel liners add weight to the tank and are subject to corrosion and embrittlement upon exposure to water and hydrogen sulfide contaminants in the methane gas. Therefore it would be desirable to provide storage tanks with liners which are comparatively light and more resistant to methane contaminants and still provide good barrier to compressed natural gas.